I had one of these, terrible dirt bike, but would be a fun dualsport!
What is done already? Mine was absolutely gutless with the stock exhaust. Get something much more open. It's been a while, and I can't remember what carburetor is on this bike. Get a 41mm FCR Keihin for sure, best carb out there! I don't think anyone offers a cam for these, so baring a custom grind.....I would avoid a big bore, you have a reliable chrome bore, and such, don't mess it up.
I would be looking to get 11-12 to 1 compression, clean up port the head, an FCR carb, and good exhaust. Don't know what else you could do!?!
Just IMHO

Since expense is not a big issue you can start at the bellmouth and end at the silencer!

I would advise some caution in your search for big Hp gains. Since a single makes all its power in one huge combustion pulse it stresses internals more than much more powerful multi-cylinder engines. You can very quickly cross the line from reliable power to short fuse power and that is an expensive and time consuming line to cross.

Back to engine mods. There are 3 ways to increase power for an engine:

1. More displacement. This is a somewhat easy route but is limited by the physical engine component sizes: liner thickness and spigot size limits overbore size and crank to deck height limits increased stroke. Also, increasing component sizes increases internal stresses so you may have to lower peak revs to compensate. As you are replacing the reciprocating parts it can be an semi-expensive route. For over bores if there is enough thickness not to require a sleeve I like the Nikasil plating technique. The addition of a sleeve can reduce heat transfer and is one more part interface that can cause problems.

2. Higher RPM. This is a deceptively easy way to increase power. Change cam timing and you engine will shift the torque curve higher in the RPM range which has the effect of producing more power. The issue is that as RPMs increase internal engine stresses increase dramatically. Strong cranks, rods and light pistons are necessary if this is the route taken. This is an expensive route and usually requires revised intake and exhaust plumbing to be effective.

Both of the above techniques will require a balanced approach and subsequent engine tuning to realize the most gains from the new parts. Above all remember that even though an engine consists of many separate parts it operates as unit. In the end you have to get the air in through the carb and out the exhaust. Increasing the bore/stroke for increased displacement may not do much if you leave the same sized ports, cam, carb, and exhaust. A big cam will not show its maximum gains if it is not coupled to appropriate sized valves and ports. Balance is the key here. An engine tuned properly from the tip of the bellmouth to the end of the silencer will produce a nice wide powerband with no dips or spikes. Also, the end use is something to consider. Huge top end power numbers and a crappy midrange will make a horrible street bike unless it is a stop light drag bike.

3. Increased efficiency. This is the legendary free lunch. Crankcase breathing improvements can make a big difference here. Any pumping that goes on in the crankcases is lost power pure and simple. Running exhaust suckers or flapper valves to run a slight vacuum in the cases can release free Hp, reduce operating temps, and stop gaskets and seals from weeping oil. Some bikes have small breather lines that you can hear the restriction on when turning the engine over by hand without a spark plug. That sound is lost power. Optimizing cooling and oil lines for minimal flow resistance are small gains that also reduce stress on the oil which is very good. Increasing compression ratio is also a very good all-around change as it makes the engine operate more thermodynamically efficient across its RPM range. The limiting factor is fuel quality but 11-12:1 is reasonable these days for street fuel.

As a last word, you will need to do dyno work to get any modded engine running optimally. Seat of the pants evaluation is just not good enough. Cam timing, jetting and ignition timing need accurate feedback to optimize. Sometimes tuning can put a dip in the torque curve but what the rider feels is a huge power hit as the engine comes out of the dip. The rider may think the engine is making big top end power because of the big hit but in reality it is making the same max power but less midrange.

For your approach I would use a tuner that can offer a package for your engine that stands behind the reported power gains. A small displacement increase, massaged ports, offset timing chain sprocket to tweak the cam timing, revised exhaust and jetting as necessary can transform an engine's characteristics. Hopefully for the better!

Iv'e been thinking about re-styling my xl500s to look more like an old school scrambler. I particularly like the lines of the high pipes on a Norton P-11 and was wondering what it would do to the perfrmance of my xl if I don't merge the header pipes and took one back on each side. If your not familair with this engine it is a four valve single cylinder with a twin port exhaust. I am curious as what to expect in the way of perfrmance and sound, any thoughts?

>>I particularly like the lines of the high pipes on a Norton P-11 and was wondering what it would do
>>to the perfrmance of my xl if I don't merge the header pipes and took one back on each side.

To do this 'properly' you'd need to keep the lengths of the pipes and mega the same but decrease the diameters appropriately. I ran a Rotax with a dual port head so know what the setup looks like. I'd use the diameter of the pipe coming out of each port for the run back to the mega and I guess scaling the mega (if there is one) by the ratio of original dual primary tube diameter to new (smaller) tube diameter.

I remember a guy named Dave who ran a Can-Am Sonic in AHRMA S.O.S., The Sonic uses the 4-stroke Rotax single and he made an exhaust for it that had one ports 'pipe running down under the motor and the other running high down the side .Both with megaphones.

He said a bunch of people told him it wouldn't work.

He also said they were wrong.
He flew on that bike. It kind of looked out of place with the dirt plastic but, it was fast.

__________________
RR's Catnip Hill to Peoria ___Loopin' Seattle to WestFest
It started with some beers __1500 miles to the Dentist
Skeedaddle to Seattle______ A 30 year old on a Three Flags Run

If I can ask several questions
a.Would the 70 degree fe570 have worked better than rotax/ducati as a basis for high powered single from a theoretical standpoint .
b.Would changing from a 2 liter air box to a snorkel with approximately same volume change reversion and subsequent mixture strength ? ie sv650 with super wide tank
c.frictional and pumping losses versus the gain in power from multiple cylinders and more intake opportunity ,is there a rule of thumb or equation to use .

My question pertains to leading link front suspensions. I want to build a set for my hacked Kaw Voyager 1200 and want to know what type of material to use. I've heard that DOM tubing is good enough and I've heard that chrome alloy is the way to go. What considerations regarding welding ? Do welds have to be treated any special way? Any important/special/ critical things to consider when designing a leading link front suspension?

a.Would the 70 degree fe570 have worked better than rotax/ducati as a basis for high powered single from a theoretical standpoint

I started the project in 1999 just before the big 4 stroke dirtbike wave so the question is moot. Would I design a new single around a new dirtbike engine? No. These new engines are very light and not too durable in a roadrace application. The rotax is a big old heavy lump and did not give us any bottom end structural problems until we reached nearly 80 wrhp. We had a few 426 and 450 based racers with built engines tested on the same dyno and they fell FAR short of what my engine was producing. I see the dirt bike based racers as more of a super 125, especially since they usually run 125gp sized tires and rims. I ran 250gp sized tires and would quickly shred a 125gp size rear. I still have a bug to finish the single project and my plan is to build a billet bottom end and crank for a new ducati head. After the v4 a single should be a breeze..... The chassis for the v4 is the same as for the single so once I get enough spare chassis parts and extra time (maybe the next lifetime!) another killer single will roar.

b.Would changing from a 2 liter air box to a snorkel with approximately same volume change reversion and subsequent mixture strength ? ie sv650 with super wide tank

A 2 liter airbox is pretty small to begin with so I'm not sure what the effect of the changes would be. Dynamic effects of ram/fresh air intakes systems are not so easy to predict. I do know from experience that fuel injected throttle bodies with a shower injector like a big airbox with plenty of still air. Air inlet should start relatively small (inlet for a 260hp motoGp bike is only about 3" in dia) and then in a long reverse tapered snorkel gradually expand to slow the air down. I think the max angle of taper should be around 7 degrees per side. Any bigger taper will cause separation and result in a very inefficient air intake. Then have it enter the airbox away from the throttle body and make sure you don't have an air current going across the top of a bellmouth.

c.frictional and pumping losses versus the gain in power from multiple cylinders and more intake opportunity ,is there a rule of thumb or equation to use .

Yes, more. Car guys seem to have found the efficiency point between breathing/rpm benefits and friction/pumping losses to be at 10 or 12 cylinders. Since engine physics are the same I'd think the same limit applies, which is more than any competitive bike has ever had. Honda's 5 cylinder 125cc and 6 cylinder 250 GP bikes of yore were amazing mechanical devices that ran to 20,000 (yes, in the 1960s) and were only discontinued due to regulations limiting cylinder count. Given that the base design is good, more cylinders=smaller pistons=lower reciprocating forces=higher rpm=more power. And smaller bore=faster combustion=higher rpm=more power. The problem is that more cylinders=more parts=more money. And more rpm=more wear=less part life=more money. So as usual racing proves that speed costs, how fast do you want to go.

>>My question pertains to leading link front suspensions. I want to build a set for my hacked Kaw Voyager
>>1200 and want to know what type of material to use. I've heard that DOM tubing is good enough and I've
>>heard that chrome alloy is the way to go. What considerations regarding welding ? Do welds have to be
>>treated any special way?

The 'which steel to use question' always seems to pop up from time to time. For most applications usually the best steel to use is the low carbon variety, 1010-1020, also known as mild steel, and also the cheapest. A plain low carbon steel tube, either DOM or CREW, will have the exact same stiffness as an aircraft certified 4130 chrome-moly tube. In engineering speak we say that all steels have the same modulus of elasticity. Put 20 lbs on the end of different alloy steel tubes of equal size and equal length and they will all deflect the same amount. What the 4130 tube will do better is be able to be bent further before it permanently deforms. In engineering speak we say it has a higher yield strength. To continue the previous example you can put more weight on the end of a 4130 tube than a DOM or CREW tube and still have it return to straight when you take the weight off.

That's the key here. When we design bike (and most) structures the only thing we want to visibly bend is the suspension spring. In other words we're concerned with stiffness, not strength. Any good chassis design that is stiff enough will not have stresses during normal use come close to the yield point of a low carbon steel so the higher yield strength of 4130 steel is largely unnecessary. If you crash the forces are higher and you (unfortunately) see permanent deformation but as Kevin Cameron said, 'not everyone is skilled enough to crash hard enough to bend a mild steel frame but not quite hard enough to bend a 4130 frame.'

DOM and CREW steel is also more forgiving to welding technique. It is less sensitive to excessive heat input and has less alloying elements that could boil off if the steel is overheated. However, I always recommend practicing good welding techniques and only the minimal heat input needed to get proper penetration. Good welding technique is free, it's just practice, practice, practice and there is no excuse for bubble gum weld beads. Regardless of what alloy you use post weld heat treatment is only needed for some exotic aircraft and aerospace requirements. Proper welding technique goes a long way to minimizing the heat affected zone. Also, NEVER cool a weld with water or an air blast or any other method. Let welds air cool in a draft free environment. It will minimize distortion and prevent the forming of hard and brittle areas that would crack under load.

Having said all that I like to use 4130 material for my final versions. It is usually held to tighter profile tolerances and for high end stuff like I do the small extra price is outweighed by the cachet of 'chrome-moly tubing' (please shoot me now). It is also more dent resistant than mild steel when the bike is dropped on rocks or something hard.

>>Any important/special/ critical things to consider when designing a leading link front suspension?

Yes, get the details right! ;) Have nice solid link pivots and rigid links. If the links are not joined behind the wheel make sure you have a very rigid axle clamping setup to provide torsional stiffness. Be sure your geometry is correct so the bike does not behave weirdly under braking. When you move away from using telescopic forks it is a lot easier to screw things up. Once you have forks bolted on at the correct angle you're done. With link systems you can be OK at one point of suspension travel and wildly off at another.

I didn't realize at first that you were talking about the nearly horizontal-cylindered Husaberg. That is an interesting engine and one that I may have thought about using. Moving the crank that much closer to the overall bike C of G should result in a much more nimble bike, especially in the dirt. Although the overall layout would be problematic for me as with a downdraft intake port that would put the throttle body and bellmouth right where there are a bunch of front control arms. hmm. It could work but obviously needs some thought to packaging.

There's not too much open information on the design details of a PVS system but at its basic it is very simple. First, the usual PVS acronym is misleading as it should be PVRS with the R standing for return. A pneumatic valve return system has a cam with normal lobes just like a spring valve engine but they replace the steel coil spring with a mostly sealed gas cylinder with pressure that provides about the same force as a standard valve coil spring. I say mostly sealed because there is some leakage in the quest for a balance between sealing and friction loss on the valve stem seals in the gas cylinder. This is also multiplied over however many valves in the engine as each valve has an individual cylinder. So far all applications are for sprint races so they merely put in a high pressure tank with enough volume to allow for leakage over race distance. In theory you can put a small high pressure compressor on the engine for unlimited usage but then you have more mechanical power drain and compressor maintenance and possibility of failure and pressure loss which would result in dropping all the valves onto the pistons and a complete engine loss. The system is a lot less exotic than it seems and it's not more prevalent on exotic street cars because it is simply not suitable for everyday use unlike a lot of other exotic engine technologies which can make a high output engine more docile.

The reason for using a PVRS system is clearly shown in this Youtube video of a valve spring in operation: valve spring coil surging. This can be seen as the bouncing motion of the middle spring coils even as the valve is fully closed and sometimes during opening and closing too. You can see the valve tip wandering a bit laterally as a result of the surge. It is important to note that this level of surge and valve stem deflection is considered good! The key point is that the spring surge is not an issue until the extremely high engine speeds that are the sole domain of F1 and MotoGP engines. Even modern production supersport engines can rev to 16000rpm with standard steel springs. Its only in the 17000+rpm area that a PVRS, or the desmo system solely used by Ducati, are suitable.

The reason why a gas spring can cycle faster than a steel spring without internal destruction is due to the relatively simple physics of natural frequencies and resonance. The concept that a small force repeated at a specific frequency can cause large deflections is easily demonstrated by pushing a child on a swing. With a pendulum style system like a child on a swing the harmonic frequency is the square root of the length of the chain divided by the weight of the child. If you keep pushing at that frequency with a small force the swing will have a huge amplitude and your child will either be having a lot of fun or thoroughly scared depending on its disposition!

A spring may not seem similar to a swingset but from a physics/math perspective it is. If you have a weight on the end of a spring and push it, then without damping the mass will bounce up and down. So if you consider the weight to be the weight of the valve then the natural frequency of the valve-spring system will be the square root of the spring stiffness divided by the mass of the valve. What this all boils down to is that if you have a valve of a certain mass then there is a limit to how fast you can open and close it without coming afoul of these resonant issues. That is a clearly defined limit and easily designed around by tweaking valve weight, spring stiffness and sometimes most importantly by introducing damping into the system in the form of friction between the multiple springs in a multi-spring system. However this frictional damping creates heat which has to be dissipated so has limits on how effective it can be.

These techniques will get you to 16000rpm with steel springs. Once you start spinning faster you'll need a more complex analysis to ensure a good valve closing system. At those high speeds the internal forces of the spring become important. The spring becomes its own a spring-mass system that is coupled to the spring/valve spring-mass system. To determine the resonant frequency of the spring instead of using the valve as the mass you use the mass of the spring itself. Its analysis gets complicated quickly! It is this internal self-interaction of the spring coils that is the cause of the surge you see in the youtube video and the root of why a PVRS system works better at high speeds. Because a spring has a decent amount of mass concentrated in its coils there are significant dynamic effects that occur when you compress and release a spring (open and close a valve) quickly. Even if the resultant surge is not causing the valve to open and leak combustion pressure the coils slamming against each other easily create forces that can break retainers or bend valve stems.

The next sentences will tell the root of why a PVRS system works at high rpms. Sorry for the roundabout explanation but some background always helps understanding.

The active element of a spring is the spring itself. It weighs a few ounces. The active element of a PVRS system is the gas in the cylinder, not the cylinder itself. The gas weighs about .01 ounce. The equation for the resonant frequency of a spring mass system is the square root of the spring stiffness divided by the mass. That means if we reduce the mass we increase the rpms at which resonance becomes dangerous. If our engine does not rev that high then we are good. By replacing a steel spring which weighs a few ounces with a gas spring of the same stiffness that weighs hundreds of times less we move the resonant frequency of the spring itself (the one that causes surge) from roughly 16000rpm to nearly 300000rpm, high enough so that we'll never have to worry about spring surge in a PVRS.

It is interesting to note that Ducati has been using a mechanically opened and closed valve for years even on its entry level bikes with no problems. They quickly made it work at 20,000rpm in their MotoGP bike. It can be made cheaply and works well yet the corporate pride of many companies prevents them from using it in their designs. Ducati has no patent protection on it and did not even invent it so anyone can create their own version but for some reason their competitors choose to go more complex with a PVRS than acknowledge the benefits of a technology that a competitor uses. I guess even though a PVRS system seems exotic it is a simple replacement of a coil spring with a gas spring while using the same cam and since race engineers far prefer evolution to revolution it was the choice they went with.

The only real problem item in your list is #3. Paint hates to stick to dirt, oil, and improperly cleaned surfaces. If you want a good result painting then clean, clean, and before you paint clean some more.

I hate paint prep which is why I like powdercoating. I drop dirty and greasy parts off (Perfection Powdercoating, horrible website, great service) and pick up durable gleaming painted pieces. My last batch was a KTM 525 frame, swingarm, subframe, and several brackets cleaned and coated for $400. Other vendors should be similar. Not cheap but very durable and extremely chip resistant. Likely the most durable type of 'paint' but definitely not the cheapest.

For the cheapest it is hard to beat a rattle can job. Its not the most chip resistant type of finish but it is cheap and can look good if done carefully. Given proper cleaning and prep and good technique it can end up with very good results. You don't have to be a great painter but you do need to take care and time if you want good results. If you do a thorough strip and cleaning of the parts followed by a couple of coats of primer, then color, then clearcoat, you will end up with a good looking and somewhat durable finish. Its better to apply several thin coats instead of fewer heavy coats. Buy the same brand primer, color and clear and follow the instructions on drying and recoating. Don't hold the can too close to the part, move it quickly and don't dwell.